Take a multi-layer PCB. Drill a hole through it. The inner copper layers are there, but the hole wall is bare epoxy—no connection between layers.
Electroplating fixes that. Put the board in a copper bath with anodes on both sides. A PCB plating rectifier applies DC current. Copper ions plate onto the hole wall and the surface traces at the same time. Now the top layer connects to the bottom layer through that hole. Do that for a few hundred holes per board, and you’ve got a working circuit.
Rectifier stability matters a lot here. If the PCB plating rectifier output jumps around, hole wall thickness gets uneven. Thin spots crack under thermal cycling. Board fails later in the field. Seen it happen.
For outer layer traces, there’s another trick. Plate tin or tin-lead on top of the copper. That plated tin acts as an etch resist—you etch away the exposed copper, then strip the tin off. What’s left is your circuit pattern.
Edge connectors need hard gold over nickel. Wear resistance for plugging and unplugging. That’s electrolytic too, so you still need a low-ripple PCB plating rectifier.
Common problems in PCB plating: uneven thickness from poor current distribution. Burning at board edges from too much current. Voids in through-holes from PCB plating rectifier ripple or bad bath agitation. Operators cut cross-sections regularly—slice a hole open, look at the copper wall under a microscope.
No electroplating, no reliable multi-layer PCBs. Simple as that.
